Process



. 1,624,147 R. W. POINDEXTER, JR., ET AL PROCESS OF' PREPAR'ING ALKALIMETAL CYANIDES April 12, 1927;

Filed April 17 1926 Patented Apr. 12, 1927. i'

UNITED STATES PATENT OFFICE.

ROBERT W'. POINDEXTER, JR., OF LOS ANGELES, AND PAUL T, DOLLEY, OF LOSANGELES COUNTY, CALIFORNIA, l.ASSIIG.`L\TO'.RS TO CALIFORNIA CYANIDECOMPANY, INCOR- PORATED, OF NEW YORK, N. Y., A COREORATION OE'DELAY/VARIE.

PROCESS F PREPARING ALKALI-METAL CYANIDES.

Application filed April l?,

rThis invention relates to the production of high gade alkali metalcyanides by causing hydrocyanic acid to react with alkali metalcarbonates.

It has been known for a. long time that hydrocyanic acid can bc made toreact, to a limited extent, with sodium carbonate 'in aqueous solution.Thus, it hydrocyanic acid be added to a solution of an alkali metal icarbonato or it gaseous hydrocyanic acid be bubbled into such asolution, a certain Iamount oi' alkali metal cyanide will formed.However, such reactions are tar 'from complete and do not otter asatisfactory `method ot preparing alkali metal cyanides in solid torni.A`To the tact that the reaction is incomplete is added the diiiicultythat a large amount of the hydrocyanic acid polymerizes and the furtherWell-known ditiliculty of satisfactorily evapointing` solutions o sodiumcyanide.

The production of alkali metal cyanides, by passing hydrocyanic acidover an alakli metal compound, such the carbonate, at a temperature of200 to 500 C., has also been sugigested. lCertain diliicnlties appear,however, when an attempt is made to carry out this reaction and theseditiiculties have prevented the successful commercial development ot theprocess of producing cyanides from the alkali metal carbonates. Inparticular, it has been dithcult or impossible to produce cyanides ofhigh purity by the process described.

lt is the object of the present invention to provide a successful andcommercially practicable process ot producing alkali metal cyanides insolid form.

Other objects and advantages of the invention Will be apparent as it isbetter understood by reference to the following specili cation andaccompanying drawing, in wh i ch F l is a` vertical section through anan paratus adapted tor use in the practice ot' the invention; and

Fig. 2 is an enlarged sectional View oi the inlet through whichhydrocyanic acid is introduced into the converter.

Vie have discovered that itis possible to produce alkali inetal cyanidesof a high degree ot purity by passing hydrocyanic acid into a fusedmixture ot' alkali metal salts ,in which carbonates predominate. Hydron1926. Serial No. 102,612.

cyanic acid is very rapidly absorbed by alkali metal carbonatos in suchfused baths. rThe composition of the bath used may be varied Widely solong as itcontains one or more alkali metal carbonatos as its activeconstituents; It is, in fact, very desirable to use a bath containing;`other constituents rather than a bath composed entirely ot a singlealkali metal carbonate such as sodium carbonate or potassium carbonato.rihe reason 'for this is that the final production ont alkali metalcyanide proceeds with good ctiiciency when the temperature of the meltedmaterial during; the introduction of the hydrocyanic acid is maintainedat a comparatively loiv point. It is, in fact, desirable to maintain thetemperature at as lovv a point as will permit the bath to remain fluid.vIt is possible, nevertheless, to operate with a bath ot a slightlypasty consistency so long,- as the hydrocyanic acid can bubble into itand thereby maintain a reasonable degree of mixing. life have found atemperature oit 550 to 6500 C. satisfactory when the melt consists ot amixture of sodium carbonate and sodium cyanide. The process Will operatesatisfactorily at higher temperatures but the etiiciency, based on HONused, Will be somewhat lower. Under cert-ain conditions a. troublesomefoaming ot the bath takes place. We have observed that this isinvariably due to impurities in the bath and.l in particular, tosuspended particles of solid 1n atter such as carbon. Such particlestend to rise as a foam and it this foam be skimmed from the top of 'thebath this trouble is thereby eliminated.

T he addition oi' other salts to a single alkali metal carbonate may bemade tor the purpose of reducing the temperature of fusion. It isfrequently advantageous to add, as a primer, a certain amount of thecyanide ot the saine alkali metal whose car bonate it is desired toconvert to cyanide. Thus, when using sodium carbonate, approXinl-ately20% oit sodium cyanide may advantageously be added, since such additionmay greatly reduce the melting point ot the sodium carbonate. The sodiumcyanide used tor this purpose Will, ot course, appear in the finishedproduct and Will not have the effect ot reducing its purity. Othersalts, such as sodium chloride, may be used in case a finished prtufinctcmitaining, for instance,

sodiumy chloride is desiied.- Or the hydroxide of thealkali metal Whosecarbonate it is desired to convert, may be added for the purpose ofreducing the melting point of the carbonate. In case a hydroxide isused, it will also be converted to cyanide and therefore, will not lowerthe purity of the final product. Oil a mixture of alkali metalcarbonatos such as sodium carbonate and potassium carbonate may be used,since such a mixture fuses at a lower ten'ipe"atu.re than either singleconstituent.

Then hydrocyanic acid is added to analkali met-al carbonate underconditions such as .those described, several reactions take place. Theprincipal reaction the direct production of alkali metal cyanide, forexample, inthe case of sodium carbonate:

Secondary reactions may then take place; thus the water, resulting fromthe first reaction, may react with sodium cyanide to form sodium formateand ammonia:

The ammonia so formed mayv then react with a further amount of sodiumcarbonate to produce sodium cya-nate, sodium hydroxide and water inaccordance with the following reaction :cr

A further reaction which may occur is the decompositionofsodium cyanateinto sodium cyanamid and carbon dioxide as fellows:

ZNaONO-NaZCNg CO2 Inl addition to the reactions.mentioned, We haveobserved the formation of sodium ferrocyanide, when using iron or steelmelting pots or pots composed of an alloy which contains iron. Ne donotknow the exactlna-nner in which this latter reaction takes place, but itisapparent that the meltingpot' itself orthe sheath of the HCN inletpipe isithesource of the iron which enters into the reaction.

From the above itwill be seen that the reaction ybetween an alkali metalcarbonate and: hydrocyanic acid is somewhat complicated.- Fortunately,however, each of the three substances formed in addition to sodiumcayanide, namely sodium cyanate, sodium cyanamid and sodiumferrocyanide, may be easily converted into sodium cyanide. Tliius, it iswell known that sodium eyanate will react. with carbon at teimieraturesin excess fof 8509' C. to produce sodium cyanide in the .followingmanner:

bon to yform sodium cyanide at a somewhat lower temperature than thatrequired for the reduction of sodium cyanate. The equation of thisreact-ion is as follows:

NagCNZ -I- C 2NaCN Sodium it'ei'rocyanide, as is also well known, willyield sodium cyanide, on heating, in aicordance with one or the other ofthe following` reactions, depending on whether the ferrocyanide isheated alone or in the presence of an alkali carbonate.

NaiFe(CN)- 4NaCN -I-Fe +2() -l- N2 NaFc (C N) a+ Na2CO3 NaCN NaCNt)Yl-hn t Ct)3 The alkali nietal cyanate torn'ied in case an alkali metalcarbonate is present is ol: course, available for reduction to alkalimetal cyanide.

From the foregoingdiscussion, ily will he seen that the forii'iation ofthese secondary products during` the first stage of the process in nowise influences the final production of alkali metal cyanide, since eachand every one of them may be readily converted to cyanide. ln order tocarry out this conversion, it is only necessary to add carbon in anyconvenient form; since carbon is re quired inl two of the above-notedreactions for the reversion of the secondary products to cyanide; andthen to heat the entire batch of material to a temperature suflicient tosecure the simultaneous carrying out of the desired reactions. Vlie havefound a teinperature of 900 C. to be satisfactory. A temperatui'e of850D C. or even lower may be used with entire success provided theheating,I is continued for a sutlicient period, and conversely, asomewhat higher temperature may be used, if it is desired to hasten thereaction, without affecting the final product. The carbon reacts quitecompletely and it is only necessary to add a slight excess over theamount theoretically required. lt may happen in some cases that, even inspite of skimming olf carbon scum to prevent excessive foaming, asuiicient amount of carbon may yet remain in suspension in the moltenmaterial to eilect the conversion of cyanates and cyanainids tocyanides. fln such cases it is obvious that the further addition ofcarbon may be omitted. 'lf he inal product is, of course, obtained inthe liquid state, and if the process has been properly carried out willconsist -o'l nearly pure alkali metal cyanide, unless other non-rerntivesalts, such as chlorides` have been purposely added or unless such othernon-reactive salts may have been present as impuritici-i4 in the alkalimetal carbonate or 'ai-bonates einV ployed. Since it is desirable 'touse a slight excess of carbon, the final product will contain suchexcess carbon in suspension. rthis may be removed by settling,` andi'lecantation or, more certainly, by filtration through a satisfactoryfiltering medium. A bed ot porous iron forms a satisfactory filter forllo the filtration of fused cyanides as is already well known. The fusedcyanide, With or without filtration, may be run into forms or moulds andallowed to solidify by cooling.

In order to make clearer the method of carrying out our process, we giveherewith the following example of the preparation of a batch of sodiumcyanide in accordance with our process. It is to be understood that thisexample is illustrative only and it is not to be taken as in any waylimiting the scope of our invention, since many details of our processmay be varied without departing from its essential features. Nor is theexample given to be understood as limitJ ing our process to the use ofsodium carboi'1ate,rsince other alkali metal carbonates will reactsiniilarly to produce the correu spending alkali metal cyanides.

For the purpose of fusing the alkali metal carbonate, (in this casesodium carbonate was used), Ywe enlployed a cast metal inciting pot withan approximately hemispherical bottom. This pot was of such size as tohave a working capacity of 2500 to 2800 pounds of melted cyanide, Thisparticular pot was composed of a heatresistant alloy consistingessentially of a mixture of iron, nickel and chromium. We have found,however, that iron or steel melting pots may be used with equal success,the onlyV difference being that they oxidize more rapidly on the outsideand hence show a shorter life than a special, heat-resistant alloy. Thispot was supported in a briclcworlr furnace and suitably heated bynatural gas.

In this pot we placed 463 pounds of a somewhat crude commercial sodiumcyanide, whichv contained., when melted, 87.8% of actual sodium cyanide.The principal impurity in this sodium cyanide was sodium carbonate. `Assoon asthis sodium cyanide was fused, we began running hydrocyanic acidinto it. The hydrocyanic.` acid was introduced through a copper tubewhich was protected from the action of sodium cya nide by an externalsheath, consistingT of an iron pipe, as described in detail elsewhere inthese specifications. Vite do not know with certainty whether' thehydrocyanic acid was entirely vaporized within the tube or whether aportion of it entered the fused batch in liquid ferm and was thenvaporiaed by contact with the fused material, but consider the latter tohave been more probable. As soon as the flow of hydrocyanic acid hadbeen started, the addition of sodium carbonate to the batch wascommenced. Commercial soda ash was used. The addition of soda ash wascontinued as rapidly as was possible Without causing the batch to freezeup, or become solid, through the chilling effect of the cold soda ash.lVe had found by previous experiments that this method ofgraduallyadding the soda ash was somewhat more satisfactory than meltning the batch as a whole, before commencing the addition of HUN,although the latter me'l'iod may be practiced with equal success so faras the quality of the final product is concerned. 1809 pounds of sodaash was added in all. After the addition of soda was coinplced, wecontinued to pass in hydrocyanic acid. The addition of hydrocyanic acidwas controlled by taking samples of fused material and analyzing themfor sodium carbonate. As the addition of hydrocyanic acid proceeded theamount of carbonato present progressively decreased and when only 0.5%of sodiun'i carbonate remained, the fiow of hydrocyanic acid wasstopped. '.lhe total amount of hydrocyanic acid (00400"0 HGN) run in was1,117 pounds. y

lo the batch was now added l. pounds oli' pulver-ized hardwood charcoal.rlhe batch was then heated to a temperature of S" C. in order to carryout the conversion of sodium cyanate, sodium cyanamid and sodirnnferrocyanide to sodium cyanide. A reasonable degree of care niust betaken in carrying out this heating up of the batch, since if the heat iscarried up too rapidly, particularly after Ii'00O C. is reached, aconsiderable amount of foaming' may take place whichmight result inoverflowing the melting pot. Ilhis foaming is due to the evolution ofgas and indicates that the desired reactions are taking place. Duringthis stage ofthe process, a certain amount of sodium carbonate isregenerated due to side reactions. r lhe batch was, therefore, cooledagain to a ten'iperature of t300" C, and a further addition of M9 poundsof hydrocyanic acid of the saine grade of purity was made. lll'ieaddition of this second quantity of hyw drocyanic acid was controlled inthe same manner, i. e., by taking samples and analyzing them for sodiumcarbonate. In this case the addition of hydrocyanic acid was continueduntil no sodium carbonate could be detected in the last sample taken.Since the batch was :found to still contain sufficient carbon, nofurther addition of charcoal was made. 'llhc batch was then againheated, this time to 8700 C., in order to coi'ivert sodium cyanate,sodiuni cyananiid and sodium fcrrocyanide to sodium cyanide.

The finished product in the fused state showed the following analysis:

NaCll 9st. 8% NdQCOS 3. OV(1 NaOH 1. 0% NaCNO 9 BMGN., Trace Nae CN) GNone Vvlater insoluble .2% Na Trace NaCl 3% The fused inaterial'wasliltered through a porous iron filter, in order to remove carbon, andWas then allowed to solidify, by cooling. rlhe linished product wasperfectly white, of excellent appearance, and showed an analysis of94.8% NaCN. A total weight oflt pounds of finished product was secured.ln addition to this, there remained in the melting' pot a residue of 185pounds .of a mixture of sodium cyanide and carbon containing 68.4% ofsodium cyanide and an additional similar residue on top of the filterWeighing 335 pounds and containing 81.01% of sodium cyanide. The sum ofthe Weights ofthe finished product, plus the weights of ythese residues,was equivalent to 99.5% of the theoretical Weight yield, based on thesum of the weights of sodium can bonate plus primer' sodium cyanideemployed. The total amount of sodium cyanide'in the product, plusresidues, corresponded toayield of 67.3%', based on the hydrocyanic acidused. Other batches have resulted iny efficiencies, based on HCN used,as high as of the theoretical. Vile have succeededv in producing, by theprocess described, a iinished product containing 98% of sodium cyanide.

A The process as herein described can be employed` to produce alkalimetal cyanides from mixtures containing alkali metal carbonatesandcyanides, and it ran be employed, consequently, in increasing thecyanide content of impure cyanide `materials Where the principalimpurity consists of an alkaliimetalcarbonate. Low grade alkali metalcyanides can thus be converted into cyanides of relatively high purity.The operation of the process for this purpose need not be variedsubstantially from the operation described'for the purpose of producingcyanides from alkali metal carbonates.

The preferred apparatus for the practice offthe process is illustratedin the accompanying drawing, in which 5 indicates a converter which maybe constructed of iron or steel vbut is made preferably of aheatfresistantl alloy consisting essentially of iron, nickelandchromium. The latter material is preferred because it resists oxidationby the heating gases Which Contact with the exterior surface. Theconverter -5 is mounted in a suitable furnace 6 of brickvvork land maybeheated by suitable burners any suitable source. The molten cyanide isdelivered by the pipe 11 into a filter .12 which may be constructed ofiron, steel or the alloy of iron, nickel and chromium, and is mounted inanother section of the furnace (S which is also adapted to be heated bymeans of suitable burners. rlhe lilter is closed by a top 13 which isprovided With ya manhole 141 and a cover 15 to permit. access forcleaning. The lower part of the lilter is lilled with a bed lb ofsuitable lltering material such as iron turnings or borings 'lhe moltencyanide passes through this bed to an outlet pipe 17, the solidimpurities, principally carbon, being retained by the lilter so that themolt-en cyanide can be Withdrawn in,l a substantially pure condition.The cyanide is delivered by the pipe 17 to a` casting apparatus orpellet. machine in which the product is solidified in suitable form forcommercial transportation and use. lwlydrocyanic acid very readilydecomposes when exposed to heated iron. A large amount of carbon resultsfrom the decomposition and in the event that a tube composed simply ofiron is used to introduce the hydrocyanic acid it would be quicklystopped up with a deposit of carbon. There would be in addition a lossof hydrocyanic acid resulting from the decomposition. Copper does nothave this effect on hydrocyanic acid even When hot. Copper is, however,rapidly attacked by fused alkali metal cyanides. A plain copper tube isnot adapted, therefore, for the introduction of the hydrocyanic acidinto the charge.

We have found it desirable to use a coinkposite tube for the purpose ofintroducing the hydrocyanic acid into the converter. The tube 10 iscomposed ofan inner tube 18 of copper and an outer sheath 19 of iron.rlfhe inner tube of copper should not be eX- posed, however, to themelted cyanide and We employ, therefore, a tip 2O which is made of amaterial Which neither decomposes hydrocyanic acid, nor is attached by`fused alkali metal cyanides, for example,

carbon.` This tip is secured to the end of the .copper tube and tstightly against the iron sheath so that the fused cyanide cannot leakinto the space between the iron and copper tubes and come in contactthereby with the copper. The outer' sheath is not aii'ectcd by thecyanide and the l'lydrocyani 1 acid is delivered through the copper tubeand thc carbon tip into the molten mass of 'alkali metal cyanide andcarbonate without decomposition. We can, therefore substantially avoiddestruction of the hydrocyanic acid within the tribe and We avoiddestruction of the tube whereby it is introduced to the molten bath. Theapparatus is adapted, consequently, for successful and continuedpractice of the process.

The principal advantages of the process Sli have been described hereinand others Will be readily apparent. Various changes can be made in thedetails of the operation and in the structure of the apparatus employedther-ein Without departing from the invention.

1. The process ot preparing alkali metal cyanides, which comprisesintroducing hydrocyanic acid into a. molten mass containing an alkalimetal compound apable oli le actingl therewith.

2. The process ol preparing mixed alkali metal cyanides, which comprisesintroducing hydrocyanic acid into a molten mass, containing a mixture ofalkali metal con'ipounds capable of reacting therewith.

3. The process ot' preparing alkali metal cyanides, Which comprisesintroducing hyH drocyanic acid into a molten mass contaiin ing an alkalimetal carbonate.

4. The process ol preparing alkali metal cyanides, which comprisesintroducing hy drocyanic acid into a molten mixture oi alkali metalcompounds includingl an alkali metal carbonate.

5. The process ol preparing alkali metal cyanides, which comprisesmaintaining a mass containing an alkali metal compound capable ofreacting with hydrocyimic acid at the lowest temperature at which itwill rei'nain molten and introducing hydrocyanii-y acid into the moltenmass.

6. 'lhe process of preparing alkali metal cyanides, which comprisesmaintainingl a mass containing an alkali metal carbonate at the lowesttemperature at which it will. remain molten and introducing liydrocyanicacid into the molten mass.

7. The process ol preparing alkali metal cyanides, which comprisesn'iaintaining a mixture ot alkali metal compounds including an alkalimetal carbonate at the lowest temperature at which it 'Will remainmolten and introducing hydrocyanic acid into the molten mixture.

8. The process oli preparing alkali metal cyanides, which comprisesheating a mass containing an alkali metal compound capable of reactingwith hydrocyanic acid to a temperature between 5500 and G500 C., atwhich it is molten and introducing hydrocyanic acid into the moltenmass.

9. The process ot preparing alkali metal cyanides, which comprisesheating a mass containing an alkali metal carbonate to a temperaturebetween 550o and 650 C., at which it is molten and introducinghydrocyanic acid into the molten mass.

10. The process of preparing alkali metal cyanides, Which comprisesheating a mixture of alkali metal compounds including an alkali metalcarbonate to a temperature between 550 and 650 C., at which it is moltenand introducing hydrocyanic acid into the molten mass.

l1. The process of preparing alkali metal cyanides, which comprisesheating a mass containing an alkali metal compound capable oi' reactingwith hydrocyanic acid to a temperature at which it is molten,introducing hydrocyanic acid, adding carbon to the mass and raising thetemperature of the mass to decimipose products ol the reaction otherthan the cyanide.

l2. rlhe process oi' preparing alkali metal cyanides7 which comprisesheating' a mass containing an alkali metal carbonale to a temperature atlwhich `it is molten.) introducing hydrocyanic acid, adding carbon tothe mass and raising the temperature of the mass to decompose productsof the reaction other than the cyanide.

13. 'llhe process olf preparing alkali metal cyanides7 which comprisesheatingl a mikh ture oi? alkali niet-al compounds containing' an alkalimetal carbonate to a `temperature at which it is molten,introducinghydrocyanic acid, adding carbon to the mass and raising thetemperature oi the mass to decon'ipose products oil the reaction otherthan the cyanide.

lll. 'lhe process oi" improving the quality ot alkali metal cyanidescontaining an alkali metal carbonate as an impurity, which comprisesintroducing hydrocyanic acid into a niolten body of the impure cyanide.

l5. The process of improving the oi alkali metal cyanides, containingture of alkali metal carbonatei.` as an impurity, 'which comprisesintroducing hydrocyanic acid into a molten body of the impure cyanidematerial.

lll. mhe process of improving the quality oi all-:ali metal cyanidescontaining an alkali metal carbonate as an impurity, which comprisesiintroducing` hydrocyanic acid into a molten body ot the impure cyanide,adding carbon to the'molten mass and raising the ten'iperature ol themass to decompose products of the react-ion other than the cyanide.

17. 'lhe process of improving the quality oi alkali metal cyanidescontaining an alkali metal carbonate as an in'ipurity7 which comprisesintroducing hydrocyanic acid into a body ot the impure cyanide while thelatter is maintained at a temperature between 5500` and 650o C. at Whichit is molten.

ln testimony Whereoi We aiiiX our signatures.

ROBERT W. POINDEXTER, JR. PAUL T. DOLLEY.

quali ty a mixH

